Properly designed substation grounding is intended to provide adequate safety and reliability to workers against unsafe potentials. Step and touch potential coordination depend on the permissible current by body weight, the fault clearing time, body resistance and earth resistance underfoot. Stressing potentials arise at many locations during normal operations, such as substation equipment cabinets that must be touched, disconnect switch operating handles and perimeter fence gates. During construction, many more touchable hazards arise, including the installation of new grounding conductors, station control wiring and the installation of bolted structures. Many of these activities include hand-to-hand touch potentials which do not benefit from the additional resistance of underfoot soil. A surface stone layer is not likely to be present; staff may be working in water filled trenches, and potentials can be transferred beyond the existing grid through safety grounds to power tools.
This research project examines various construction activities and hazards that arise during such work. It summarizes existing practices and explores a wide range of tools and procedures that could reduce step and touch potentials. It also quantifies the efficiency and hazard reduction value offered by differing mitigation methods and provides recommendations to improve touch coordination during substation expansion.
Substation Expansion, Touch Potentials, Step Potentials, Grounding Practice